It is known in the art to apply printed adhesive-backed labels to containers for products such as liquid soap and detergent, shampoo, food products and vitamins to name only a few. Self-adhesive labels are generally made in such a way as to require the removal of a “release paper” from the adhesive side of the label before it is applied to the container. Removal of the release paper exposes the pressure sensitive adhesive, permitting the label to be applied to the container. Slight pressure is then applied to create the adhesive bond.
The term “pressure sensitive adhesive,” as used herein, refers to an adhesive which bonds to an application surface as a result of applied pressure as opposed to the evaporation or absorption of a solvent to form a solid material bond.
Adhesive-backed labels and the like typically comprise the laminated combination of a printable face stock, a pressure sensitive adhesive on the back or reverse side of the face stock, a silicone layer and a backing paper to which the silicone layer is relatively strongly bonded. The face stock can be transparent or opaque. Opaque stock can be printed on both sides while transparent stock can typically only be printed on one side. Double-side printing is desirable where, for example, the printed label is applied to a transparent container such as a plastic bottle filled with a relatively transparent fluid such as liquid soap or detergent; i.e., the printing on the back or reverse side of the finished, applied label can be viewed through the container and the product to provide a pleasing effect or additional information about the product and/or its manufacturer.
The adhesive which constitutes a layer between the face stock and the silicone is typically water based and, therefore, requires relatively long air drying time. The backing paper is usually “glassine paper,” a material which, like the face stock, is available in rolls and accepts the silicone layer which is necessary to produce the release effect. The laminated combination of glassine paper and cured silicone is referred to as a “release paper.”
The prior art method of manufacturing pressure sensitive adhesive labels and/or face stock typically involves the step of coating a glassine paper with silicone and hanging the de-reeled, silicone coated paper on a suitable support to cure.
After this first step, the cured release paper is re-reeled and taken back to the entry point of a second lamination process in which the adhesive is applied. Once again the de-reeled, adhesive coated release paper is hung out in the 200 ft. structure to cure. After curing it is re-wound and again subjected to a lamination step to add the printable label stock.
After this manufacturing process has been completed, the re-reeled laminated label stock is provided to a printer who again de-reels the stock to print on the indicia necessary to create a label.
The prior art manufacturing method described has a number of drawbacks. In the first place, the process described above requires a relatively large structure with a controlled atmosphere; i.e., adequate systems to control humidity and temperature within the curing structure. Secondly, the prior art method described above requires numerous de-reeling and re-reeling or re-winding steps and multiple lamination steps.
Thirdly, the prior art method described above makes it particularly difficult to print on the reverse side of the label stock; i.e., the side to which the adhesive is relatively strongly bonded. Where reverse-side printing is desired, the completed, pressure sensitive adhesively-backed label stock must be de-laminated and the printing must typically be applied over the adhesive. This gives rise to blurry, less definite printing and typically requires protection of the printed adhesive through the addition of, for example, UV varnish or UV glued film.